1. Field of the Invention
The present invention relates generally to the fields of cancer biology and molecular biology. More particularly, it concerns methods of determining prognosis in a subject with a hyperproliferative disease that involve determining expression and/or function of 14-3-3 zeta in the subject. It also concerns methods of making a pharmaceutical agent that modulates apoptosis, including the steps of obtaining one or more candidate, testing the one or more candidate substances to determine their ability to modulate the expression and/or function of 14-3-3 zeta, selecting a candidate substance determined to modulate the expression and/or function of 14-3-3 zeta, and making a pharmaceutical composition that includes the selected candidate substance. In addition, the present invention concerns methods of treating a subject with a hyperproliferative disease, including making a pharmaceutical agent by any of the methods set forth herein, and administering the pharmaceutical agent to a subject.
2. Description of Related Art
The 14-3-3 proteins constitute a family of highly conserved dimeric proteins that are ubiquitously expressed in eukaryotic organisms (Aitken et al., 1992). These proteins were originally isolated in 1967 (Moore and Perez, 1967). The name “14-3-3” is derived from the particular migration pattern on two-dimensional DEAE-cellulose chromatography and starch gel electrophoresis (Moore and Perez, 1967). In humans, nine isoforms have been found to be encoded by seven 14-3-3 genes. The encoded proteins have a molecular weight of 29 kDa-31 kDa.
High levels of 14-3-3 proteins were originally shown to exist in neuronal tissue, and it was originally thought that they were neuron-specific (Moore and Perez, 1967). However, they have now been shown to be widely distributed and present at low levels in most mammalian tissues. Proteins that show a high degree of similarity have been cloned and sequenced from a wide range of other eukaryotic organisms including plants, insects, amphibians and yeast (Aitken et al., 1992).
The 14-3-3 family is highly conserved over a wide range of mammalian species, and the 14-3-3 isoforms can be found in an extremely broad range of tissues. There are very high levels of many isoforms in brain tissue, particular Purkinje cells in the cerebellum (Watanabe et al., 1991). High levels of beta and gamma isoforms are also found, the latter of which is believed to be specific for the brain (Isobe et al., 1991). There are also high levels of some isoforms in adrenal medulla and intestine, platelets, and testis (Ichimura et al., 1991). Other isoforms are expressed in spleen, skin, ear, and tongue (Aitken et al., 1992). Homologues of 14-3-3 proteins have been found in a broad range of eukaryotic organisms and are probably ubiquitous (reviewed in Wang and Shakes, 1996; Rosenquist et al., 2000).
Crystal structures of both the tau and zeta isoforms of 14-3-3 show that they are highly helical, dimeric proteins (Xiao et al., 1995; Liu et al., 1995). Each monomer is composed of nine anti-parallel α-helices, organized into an N-terminal and a C-terminal domain. The dimer creates a large negatively charged channel. Those regions of the 14-3-3 proteins which are invariant throughout all of the isoforms are mainly found lining the interior of this channel, while the variable residues are located on the surface of the protein (Aitken et al., 2002). This channel might recognize common features of target proteins, so the specificity of interaction of 14-3-3 isoforms with diverse target proteins may involve the outer surface of the protein (Aitken et al., 2002). The N-terminal residues of all 14-3-3 homologues are variable, and are involved in dimer formation (Aitken et al., 2002).
The known functions of the 14-3-3 class of proteins include a wide range of cell signaling processes as well as development and growth regulation. The first function of this family of proteins that was described was activation of tyrosine and tryptophan hydroxylases, the rate-limiting enzymes involved in catecholamine and serotonin biosynthesis, essential for the synthesis of dopamine and other neurotransmitters (Ichimura et al., 1988). Subsequently, it was shown that 14-3-3 could regulate (inhibit) activity of protein kinase C(PKC) (Aitken et al., 1990; Toker et al., 1990). 14-3-3 was then found to be a novel type of chaperone protein that modulates the interaction between components of signal-transduction pathways (Aitken, 1996). Previous studies indicated that different 14-3-3 isoforms have overlapping roles within cells as they bind many of the same target proteins (Yaffe, 2002).
In the mid-1990's, numerous reports showed that 14-3-3 proteins could interact with a wide range of protein kinases, phosphatases, and other signaling proteins (reviewed in Aitken et al., 2002), which implies that 14-3-3 proteins mediate the formation of protein complexes involved in signal transduction, trafficking and secretion, perhaps to bind to different signaling proteins on each subunit of the dimer, as a novel type of ‘adapter protein.’
In addition, 14-3-3 proteins play a role in suppression of apoptosis. They bind many proteins involved in regulation of apoptosis, such as BAD (Zha et al., 1996), A20 (De Valck et al., 1997), Forkhead (Brunet et al., 1999), and ASK1 (Zhang et al., 1999). Compromising 14-3-3 function by overexpression of a competitive 14-3-3 binding peptide rendered cells more sensitive to apoptotic stimuli (Masters and Fu, 2001).
One of the kinases that has been shown by the inventors to interact with 14-3-3 proteins is phosphatidylinositol 3-kinase (PI3-kinase). The PI-3 kinases represent a ubiquitous family of heterodimeric lipid kinases that are found in association with the cytoplasmic domain of hormone and growth factor receptors and oncogene products. PI3Ks act as downstream effectors of these receptors, are recruited upon receptor stimulation and mediate the activation of second messenger signaling pathways through the production of phosphorylated derivatives of inositol (Fry et al., 1994). PI3Ks have also been implicated in many cellular activities including growth factor mediated cell transformation, mitogenesis, protein trafficking, cell survival and proliferation, DNA synthesis, apoptosis, neurite outgrowth and insulin-stimulated glucose transport reviewed in (Fry et al., 1994).
The PI3-kinase enzyme heterodimers most commonly consist of a 110 kD (p110) catalytic subunit associated with an 85 kD) (p85) regulatory subunit. Recently however, three smaller regulatory subunits have been identified, two 55 kD subunits (p55.alpha. and p55.gamma.) and one 50 kD subunit (p50.alpha.) (Shin et al., 1998). Modulation of PI3-kinase activity by 14-3-3 zeta in cancer cells is not established from previous studies. (Munday et al., 2000; Guthridge et al., 2000; Liu et al., 1996). These previous studies concerned hematopoietic rather than cancer cells.
Cancer is a major cause of morbidity and mortality in the si U.S. Breast cancer, for instance, now affects as many as one in eight women during their lifetime (Ries et al., 1999; Sondik 1994). In many regions of the world, breast cancer is the more frequently occurring malignant disease in women (Forbes, 1997). Methods of diagnosing and treating breast cancer are a major research focus in the U.S.
Although many biomarkers for breast cancers (e.g. estrogen receptor, ErbB2, Bcl-2) have been discovered during the last decades, ideal prognostic factors for breast cancers are still lacking (Rogers et al., 2002). For instance, only about 30% of breast cancers overexpress c-erb2, epidermal growth factor receptor, cyclin D1, or c-myc (reviewed in Welch and Wei, 1998).
There is no clear role of 14-3-3 isoforms in human cancer. In particular, there has been no previous report on tumor promoting function of 14-3-3 isoforms in human cancers. Recently, however, loss of 14-3-3 sigma gene expression was found to be a frequent event in breast cancer (Ferguson et al., 2000). The 14-3-3 sigma isoform is believed to be responsible for instituting the G2 cell cycle checkpoint response to DNA damage in human cells (Hermeking et al., 1997; Chan et al., 2000). Although 14-3-3 sigma has been associated with tumor suppression (Ferguson et al., 2000), this function has not been ascribed to other 14-3-3 isoforms. Another study found that levels of the alpha, beta, delta, and zeta isoforms of 14-3-3 were the same in both normal and transformed cells (Vercoutter-Edouart et al., 2001). These results indicate that the precise role of the 14-3-3 family of proteins in human cancer remains ill-defined.
Therefore, the identification of the precise role of 14-3-3 proteins in human cancer may provide valuable insight that can be applied in the clinical care of cancer patients. Detailed elucidation of any relationship between 14-3-3 expression and cancer could provide new forms of cancer therapy. Knowledge of a correlation between 14-3-3 protein levels and cancer severity or cancer type could be applied in formulating accurate prognosis of cancer patients, and could also be applied in designing targeted therapeutic and preventive strategies.